Transition Metal-Catalyzed Non-Directed C-H Functionalization of Arenes and Alkanes.

Abstract

The development of novel methods to convert chemical feedstocks is desirable, as it holds the potential for valorization. These chemicals are primarily hydrocarbons and therefore, the key for their functionalization lies in C-H functionalization reactions, which are traditionally challenging. Using homogeneous transition metal complexes to facilitate C–H bond activation and functionalization is a promising method for C-H functionalization. This thesis describes the development of methods and mechanistic analysis of C-H functionalization of alkanes and arenes, both of which are the primary components of chemical feedstocks. Chapter 1 describes in detail the challenges in C-H activation and functionalization, as well as the relevant history and precedent for the work detailed herein. Chapter 2 details the development of palladium/pyridine-based catalyst systems that are highly active for the C-H oxygenation of benzene and other simple arenes. An iodine(III) oxidant or the inexpensive potassium persulfate oxidant is used. Chapter 3 investigates the mechanism of the palladium/pyridine catalyzed conversion of benzene to phenyl acetate using the iodine(III) oxidant. Detailed mechanistic and kinetic analyses were used to determine that the active catalyst in solution is a dimer with one pyridine ligated per palladium. The mechanism by which this precatalyst enters into the catalytic cycle and functionalized benzene was elucidated using kinetic analysis. In Chapter 4, a catalyst system was developed for the site selective C-H oxygenation of simple arenes. Using an acridine/palladium catalyst with a sterically bulky iodine(III) ligand, high site selectivities are obtained, favoring functionalization at the least sterically hindered C-H bond. Chapters 2-4 detail the accomplishments regarding arene C-H functionalization. However, alkanes are another abundant feedstock available whose functionalization has proved more challenging. In this context, one of the most challenging substrates is methane. In Chapter 5, the borylation of methane using Ir and Rh catalysts is explored. Methane is converted to a methyl boronic ester using a diboron reagent, and the activities and selectivities of the Rh and the Ir catalysts are compared.